The present invention relates to fluid flow control in microdevices. More specifically, the invention relates to microdevices that employ a high-pressure-capable valve structure, the valve structure optionally achieving flow path switching through rotational or linear motion.
Microfluidic devices (microdevices) hold great promise for many applications, particularly in applications that employ rare or expensive fluids. Proteomics and genomics are two important areas in which microfluidic devices may be employed. For example, many of the best-selling drugs today either are proteins or act by targeting proteins. In addition, many molecular markers of disease, the basis of diagnostics, are peptidic or nucleotidic sequences. Thus, development effort to advance the diagnostics or pharmaceutical technologies has focused on the discovery of medically important proteins and the genes from which they derive. Thus, biomolecular identification is a particularly important aspect of proteomics and genomics.
Biomolecular identification often involves separation processes such as chromatography and mass spectrometry. For example, U.S. Pat. No. 5,705,813 to Apffel et al. describes an integrated planar liquid handling system for matrix-assisted laser-desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. The patent discloses that a reservoir for receiving fluid substances may be interconnected by a microchannel to a MALDI ionization surface, wherein the microchannel comprises a separation region that may be used for chromatographic-type separations.
This approach represents an example of recent progress in microdevices that can be used, for example, as chemical analysis tools or clinical diagnostic tools. The small size of microdevices allows for the analysis of minute quantities of sample, which is an important advantage when the sample is expensive or difficult to obtain. See, e.g., U.S. Pat. Nos. 5,500,071 to Kaltenbach et al., 5,571,410 to Swedberg et al., and 5,645,702 to Witt et al. Sample preparation, separation and detection compartments have been proposed to be integrated on such devices. Because microfabricated devices have a relatively simple construction, they are in theory inexpensive to manufacture. Nevertheless, the production of such devices presents various challenges. For example, the flow characteristics of fluids in the small flow channels of a microfabricated device may differ from the flow characteristics of fluids in larger devices, as surface effects come to predominate and regions of bulk flow become proportionately smaller. Thus, means for producing a motive force that moves analytes and fluids may have to be incorporated into such microanalytical devices. This may involve forming motive force means such as electrodes, which may add to the cost of the microdevice.
Thus, flow control is an important aspect of microdevice technology. Since it is well known that the flow characteristics of fluids in the small flow channels of a microdevice differ greatly from flow characteristics of fluids in bulk, conventional wisdom dictates that valve structures that control flow of fluids in bulk are not easily adapted for use in microfluidic devices. Accordingly, a number of patents disclose various valve technologies employed in microdevices. U.S. Pat. No. 4,869,282 to Sittler et al., for example, discloses a micromachined valve that employs a control force to deflect a polyimide film diaphragm. Similarly, U.S. Pat. Nos. 5,771,902 and 5,819,794 to Lee et al. describe a microvalve that employs a controllable cantilever to direct blood flow. U.S. Pat. No. 5,417,235 to Wise et al describes an integrated microvalve structure with monolithic microflow controller that controls actuation electrostatically, and U.S. Pat. No. 5,368,704 to Madou et al. describes a micromachined valve that can be opened and closed electrochemically. Other aspects of valve operation and control are described in U.S. Pat. Nos. 5,333,831, 5,417,235, 5,725,017, 5,964,239, 5,927,325 and 6,102,068. Many of these valves are complex in construction and are incapable of the fast response times required in certain biomolecule analysis applications due to an excess of xe2x80x9cdead space,xe2x80x9d i.e., unused and unnecessary space within the microdevice.
Thus, there is a need for an improved and simplified valve structure for controlling fluid flow in microdevices without introducing excessive dead space therein.
Accordingly, it is an object of the present invention to overcome the above-mentioned disadvantages of the prior art by providing a microdevice that allows for improved fluid flow control.
Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned through routine experimentation upon practice of the invention.
In one embodiment, then, the present invention relates to a microdevice comprising a substrate and a cover plate each having a substantially planar contact surface and a fluid-transporting feature associated therewith. The substrate contact surface is positioned in slidable and fluid-tight contact with the cover plate contact surface to allow for controllable alignment between the fluid-transporting features. As a result, fluid communication is provided between the fluid-transporting features through a small area. When the cover plate fluid-transporting feature comprises a conduit, the conduit may have a substantially constant cross-sectional area. Typically, the fluid-transporting features align to form a fluid-transporting conduit having a controllable cross-sectional area no greater than about 1 mm2. Such a previously unknown small cross-sectional area allows for reduction of dead space in microdevices while providing for improved fluid flow control through mechanical actuation, typically, through a sliding and or rotation motion.
In another embodiment, the invention relates to a microdevce comprising a substrate having at least two substantially planar contact surfaces and a conduit extending therethrough to provide fluid communication between the contact surfaces. Two cover plates each having a substantially planar contact surface are positioned in substantially fluid-tight contact with the substrate. A fluid-transporting feature is associated with the first contact surface. At least one of the first and second cover plate contact surfaces is positioned in slidable contact with a substrate contact surface to allow for controllable flow path formation.
In a further embodiment, the invention relates to a microdevice for controlling fluid flow comprising a substrate and a cover plate each having a substantially planar contact surface. A fluid-transporting feature is associated with each contact surface. The substrate contact surface is positioned in slidable and fluid-tight contact with the cover plate contact surface to allow for controllable alignment between the fluid-transporting features to form an alignment-dependent variable-length flow path.